Through measuring the above/below-ground growth data of Haloxylon ammodendron seedlings at different stages in hinterland of the desert the results show that the H. ammodendron seedling growth has demonstrated different adaptation characteristics in the continued arid environment with time and space. In May, July, September and October, the growth speed of vertical root is 0.607 cm/d, 0.809 cm/d, 0.155 cm/d and 0.394 cm/d, respectively; the growth speed of height is 0.093 cm/d, 0.076 cm/d, 0.408 cm/d and 136 cm/d, respectively. It is explained that seedlings root system has the growth superiority in space. The maximum growth speed of below-ground (vertical root and horizontal root) of seedling is earlier than that of above-ground (height and horizontal of shoot). In the different periods, the vertical growth speed and the horizontal growth speed of below-ground is 2–10 times and 3–5 times than the height increase speed and the shoot growth speed, respectively. In the whole season, the growth speed of above/below-ground of seedlings shows the alternation growth tendency. At the different periods, the root/shoot ratio of H. ammodendron seedlings is 0.41, 0.3, 0.39 and 0.88. All these characteristics are the comprehensive performance of seedlings’ strategy selection to adapt to the continued arid environment.